Re: grep flip flop (range operator)

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Re^2: grep flip flop (range operator) by Anonymous Monk on Sep 13, 2012 at 07:02 UTC
Bingo. Thanks. That "Range Operators" page I have now read in my console via `perldoc -f ..` It dawned on me after posting that the first condition is never true and I came up with `$ perl -le " print for grep { my $what = scalar($Q++==0 ..($_ eq q{Q} +)); warn $what; $what } qw{ a b c Q r s }; " 1 at -e line 1. 2 at -e line 1. 3 at -e line 1. 4E0 at -e line 1. Warning: something's wrong at -e line 1. Warning: something's wrong at -e line 1. a b c Q` [download]	[reply] [d/l]
Re^3: grep flip flop (range operator) by frozenwithjoy (Priest) on Sep 13, 2012 at 07:34 UTC
To make things a bit more readable, you could use the match-once operator like this: `perl -le " print for grep ?? .. /Q/, @ARGV " a b c Q r s ___ a b c Q` [download]	[reply] [d/l]
Re^4: grep flip flop (range operator) by Anonymous Monk on Sep 13, 2012 at 07:37 UTC
Uh-oh `$ perldoc -f ?? No documentation for perl function '??' found` [download]	[reply] [d/l]
Re^5: grep flip flop (range operator) by frozenwithjoy (Priest) on Sep 13, 2012 at 07:42 UTC
Re^6: grep flip flop (range operator) by Anonymous Monk on Sep 13, 2012 at 07:55 UTC
Re^2: grep flip flop (range operator) by frozenwithjoy (Priest) on Sep 13, 2012 at 07:12 UTC
BONUS STUMPER: For all of the ones that don't print, they do print if you replace `1` with `0`; however, all elements are printed instead of stopping at `Q` (shown below). For the one that did print, the change to `0` causes it to not print. Anyone able to explain this? `a b c Q r s` [download]	[reply] [d/l] [select]
Re^3: grep flip flop (range operator) by davido (Cardinal) on Sep 13, 2012 at 07:23 UTC
`perl -E 'say "Yes!" if $. == 0;'` $. uninitialized if there's no file open for reading (undef). undef is false. In a numeric comparison, undef is promoted to zero (or conceptually better, zero is demoted to false, and undef is promoted to false). Consequently, `0 ..` is true, and the flip flop flips. If warnings were enabled you'd get one. :) Dave	[reply] [d/l] [select]
Re^4: grep flip flop (range operator) by frozenwithjoy (Priest) on Sep 13, 2012 at 07:26 UTC
Ah, yes.... and the reason it doesn't stop at `Q` is because it gets flipped right back on after `Q`. Apparently, my brain only works once per night. Thanks!	[reply] [d/l] [select]
Re^3: grep flip flop (range operator) by grizzley (Chaplain) on Sep 13, 2012 at 08:51 UTC
Whole list is printed, as after spotting 'Q' flip-flop goes to 'false' state and back to condition `$. == 0` which is all the time true, so it sets flip-flop again to true.	[reply] [d/l]